1) Storage Area Network (SAN)
A network that connects one or more computers and one or more external storage devices is called a storage area network (SAN). SAN is a computer system often used especially in the case where a plurality of computers cooperate to provide one function or where one or more computers share one mass storage device. An advantage of SAN is its high extensibility because of its easiness of later addition, deletion, and replacement of storage resources and computer resources.
2) Disk Array Device
Disk array devices are commonly used as external storage devices connected to a SAN. A disk array device is a device that includes many magnetic storage devices typified by hard disk drives.
A disk array device uses the RAID (Redundant Array of Independent Disks) technology to manage several magnetic storage devices as a set. This set of magnetic storage devices is called a RAID group. A RAID group forms one or more logical storage areas. A computer connected to a SAN performs input/output processing for these storage areas. When data is recorded in a storage area, the disk array device records redundant data in one or two of the magnetic storage devices that constitute the RAID group. At the occurrence of a failure in one of the magnetic storage devices, this redundant data advantageously allows the data to be recovered from the rest of the magnetic storage devices in the RAID group.
3) Thin Provisioning Technology
In conventional operation of a SAN, when storage volumes are mounted on a file system that is run by a host computer, an appropriate physical disk capacity needs to be statically pre-allocated. However, in such operation, a large number of steps such as stopping the system are required for increasing the capacity or for creating and deleting a volume.
As such, the thin provisioning technology has emerged. In this technology, rather than pre-allocating the physical disk capacity, storage volumes are provided in the host computer as virtual units. At the occurrence of a write operation from the host, an area is dynamically allocated from a storage resource pool. Since the predefined storage resource pool can be configured with a smaller capacity than a virtual volume, the efficiency of capacity usage is improved. In addition, since increasing the capacity of the pool does not affect the host computer, operation is simplified to reduce the management load.
4) De-Duplication Technology
This is a technology of writing data in volumes without duplication. In this processing, writing is performed in such a manner that data is recorded only if the same data as the data to be written is not stored in a write-target area. If the same data is stored, the data itself is not recorded and only the write location is recorded in metadata to avoid multiple storage of the same data. This provides an effect of reducing the used capacity compared to the case where all data is written.
A duplication check may be performed on a block basis, a file basis, and so on.
[Patent Citation 1]
U.S. Pat. No. 6,928,526